Cannot start Nightfall team via App using Xbox One.

If anyone can possibly help me out here it would be fantastic as I'm having no fun with the Destiny 2 App (Android) trying to form or join a Nightfall Team on the Xbox One.
[b]Forming[/b]
I'll start it up, set the wanted players and it'll show just fine. I'll be sat in orbit and strangers will happily join the team (on the app) yet when I invite them the yellow circle just spins and spins, but they don't appear as part of my team within game. I'll get PM's from them telling me to "Invite!" and I'll message back, "I am!". Generally at this point they just leave.
[b]Joining[/b]
I'll see a somebody looking for more members on a Nightfall run so I'll add myself. Yet nothing happens. I know they're trying to invite me mind you, as on one instance I've had somebody block me from attempting to rejoin the group, even though (on my side) I never actually received an invite nor got any further than putting my name forward. I can understand their frustration. A person arrives, yet doesn't do anything expect waste a space; though I'm not on my side.
The only Nightfall I've managed to get on was due to (thanks to PM) the team members understanding my plight and they sent me an Xbox invite via my Gamertag instead. This worked fine.
All of my privacy settings on the Xbox One are set to allow Multiplayer access and I honestly cannot work out what the issue is here. Is it the Phone App, is it the Xbox, is it me?
I must be doing something wrong though, but what!? If anyone can help, please can you let me know what settings I should be changing?
Thanks in advance.